This proposal in the broadest sense is for the study of the biogenesis of messenger RNA (mRNA) and its post-transcriptional modification by poly A polymerases. The experimental approach will examine heterogeneous nuclear RNA (HnRNA) structure, synthesis and processing into messenger RNA in a cultured mouse myeloma cell line which produces a specific mRNA for the light chain of immunoglobulins. Preparations of nuclei from myeloma cells which synthesize RNA in vitro will be used to study the polyadenylation of HnRNA and its processing into mRNA and the release of mRNA from the nucleus. A second phase of the proposal will be devoted to polyadenylation reactions with purified poly A polymerase. Purification of this polymerase from calf thymus by new affinity chromatographic techniques is in progress. Characterization of the polymerase protein and certain details of the reaction such as ease of reversibility are planned. BIBLIOGRAPHIC REFERENCES: Edmonds, M. and Winters, M.A., Polyadenylate polymerases. Prog. in Nucleic Acid Research and Molecular Biology, 17, p. 149-79 (1976). Venkatesan, S., Nakazato, H., and Edmonds, M., Preparation and properties of a poly A resin and its use in the isolation of naturally occurring poly U sequences. Nucleic Acid Res., 3, 1925 (1976).